Mini LED torch, uv

The luminous flux (lumen)
describes the total quantity of light provided (independent of the angle of beam).

The dominant wavelength
indicates the perceived colour of a source which is not monochromatic but in the CIE colour space. Most actual LEDs are near the pure colour curve but not on it. When connecting and extrapolating the points W (white) and P (sample), the intersection with the colour curve yields the dominant wavelength. The dominant wavelength can further be explained via the spectrum. After assessing the spectrum of the source using the V(λ) curve, the spectral centroid is determined. The dominant wavelength provides the most accurate information about the perceived colour of a source.